Chapter 8 weathering

Question 1

what is weathering influenced by?

Answer 1

rock type
rocks with minerals that react with water will erode faster

climate
this decides what kind of weathering will take place and the speed of it

topography
upland areas are more exposed to weathering then lowland

Question 2

describe freeze thaw action (physical weathering)

Answer 2

It occurs in upland regions where the temperature fluctuates above and below freezing point often.
For example Alpine and Arctic regions
during the day when temperatures are warmer water fills in the gaps in rocks. This water then freezes at night when the temps drop below freezing this causes its volume to expand by 9% putting pressure on the rock forcing it to open up.
then during the day the water thaws and the pressure is released
this cycle slowly weakens the rock and eventually parts of the rock break off. this is called scree
scree can be seen in the sugar loaf in Wicklow.

Question 3

describe exfoliation (physical weathering)

Answer 3

this process strips the outer layers of rocks
exfoliation occurs in areas with very high daily temperatures frequently above 40 degrees
such as the Sahara
the heating of the rocks surface causes it to expand .
but due to a lack of cloud cover and vegetation there is a huge loss of heat at night ( around 0 degrees) causing the rock surface to cool and contract
the heating and cooling do not happen evenly (see other flashcard)
eventually the outer layer of the rock peel off like an onion and accumulate as scree.

Question 4

why do the rocks not heat and cool evenly?

Answer 4

the outer layers heat and cool much faster then the internal

dark rocks absorb heat faster then light

minerals expand by different amounts

Question 5

explain carbonation

Answer 5

rainwater absorbs carbon dioxide as its falls through the atmosphere this forms a weak carbonic acid.

limestone contains calcium carbonate which reacts with the weak carbonic acid to form calcium bicarbonate.
this creates distinct landscapes called karst found in the Burren Co Clare

Question 6

explain hydrolysis (chemical weathering)

Answer 6

this happens when water reacts with the chemicals in rocks and breaks them down.
it produces a weaker and softer material then the original
this happens much faster in hot wet conditions such as the tropics
here the water seeps down deep into the rock so hydrolysis happens far below the surface it helps when the water is slightly acidic.

the feldspar in granite easily absorbs water and decays to form a new clay like mineral called kaolin this crumbs easily causing it to breakdown